The present invention relates to variants of stem cell inhibitors.
The treatment of cancer with chemotherapeutic agents is designed to attack and destroy cells which are undergoing division within the body. A side effect of such treatment is thus the destruction of normal cells, particularly the stem cells of the haematopoietic system and the epithelial stem cells which line the scalp and gut. Radiation can also cause similar destruction of such cells.
It has been proposed that in order to improve the treatment of cancers by chemotherapy it would be desirable to protect stem cells from cell cycle specific cytotoxic drugs. WO89/10133 discloses a stem cell inhibitor and describes the use of the inhibitor in the treatment of cancers. The inhibitor may be administered to a patient in order to protect stem cells during chemotherapy.
Stem Cell Inhibitor (SCI), also known as MIP1-xcex1 is a peptide of about 8 kD which forms large self aggregates, the molecular weight of which is dependant upon the concentration of SCI/MIP1-xcex1 monomers (Graham et al, 1990, Nature 344;442, Wolpe and Cerami, 1989, FASEB J, 3; 2656). It has been found that SCI/MIP1-xcex1 has a native, aggregated molecular weight of about 100 kD at 0.1 mg/ml in physiological buffers such as PBS. It has been found that diluting SCI/MIP1-xcex1 to about 20-100 ng/ml or less will bring about disaggregation of this protein.
Human SCI/MIP1-xcex1 has been cloned by us (Graham et al (1992), Growth Factors 7;151-160). The cDNA has also been cloned by Nakao et al (1990, Mol. Cell, Biol., 10;3646-58) and called LD78xcex2. A variant of the cDNA LD78xcex1 was also found, which has a very similar sequence. It differs by only 4 amino acid residues. The human cDNA and protein sequence of the factor cloned by us is shown is Seq. ID No. 1. The first 27 amino acids are a leader sequence. The mature protein starts at residue 28 (ala). The amino acid sequence of the variant found by Nakao et al is shown as Seq. ID No. 3. The leader sequence of the protein is one amino acid shorter and thus the mature protein starts at residue 27 (ala). The sequence of the murine homologue, upon which we have conducted our work, is also known and is very similar. It can be found for example in Graham et al (1994, J. Biol. Chem., 269; 4974-78).
It has been reported (Mantel et al, 1993, PNAS 90;2232) that monomeric SCI/MIP1-xcex1 is more active than the aggregated form in inhibiting in vitro and in vivo stem cell proliferation. In using SCI/MIP1-xcex1 in the treatment of humans it would be desirable to administer monomeric protein, not just from an activity point of view but also in order to provide reliable and reproducible formulations. However, it is likely that the low concentrations of SCI/MIP1-xcex1 which must be made in order to provide monomeric protein will be too low for use in practice.
We have now surprisingly found that it is possible to obtain SCI/MIP1-xcex1 variants which retain substantially the activity of the native protein but which do not form the same large aggregates. These mutants are stable as monomers or as small conglomerates (eg dimers or tetramers) at concentrations many fold higher than native SCI/MIP1-xcex1. Thus for those variants which have activity comparable to native SCI/MIP1-xcex1, the variants may have higher activity in vivo on a unit weight basis.
Accordingly, the present invention provides a Stem Cell Inhibitor protein which comprises at least one amino acid alteration from its native form which does not significantly aggregate but which retains substantially unaltered stem cell inhibitory activity. The protein may comprise either the full length stem cell inhibitor or the mature processed form lacking the leader sequence.
The invention also provides pharmaceutical compositions comprising a stem cell inhibitor according to the invention in combination with a pharmaceutically acceptable carrier or diluent, and optionally other therapeutic ingredients. The carrier(s) must be xe2x80x9cacceptablexe2x80x9d in the sense of being compatible with the other ingredients of the formulation and not deleterious to the recipients thereof.
The formulations include those suitable for parenteral (including subcutaneous, intramuscular, intravenous, intraperitoneal, intradermal, intrathecal and epidural) administration. The formulations may conveniently be presented in unit dosage form and may be prepared by any of the methods well known in the art of pharmacy. Such methods include the step of bringing into association the active ingredient with the carrier which constitutes one or more accessory ingredients. In general the formulations are prepared by uniformly and intimately bringing into association the active ingredient with liquid carriers.
Formulations suitable for parenteral administration include aqueous and non-aqueous sterile injection solutions which may contain anti-oxidants, buffers, bacteriostats and solutes which render the formulation isotonic with the blood of the intended recipient; and aqueous and non-aqueous sterile suspensions which may include suspending agents and thickening agents, and liposomes or other microparticulate systems which are designed to target the compound to blood components or one or more organs. Suitable liquid carriers include phosphate buffered saline at a pH of between 7.0 and 8.0, for example 7.4. The formulations may be presented in unit-dose or multi-dose containers, for example sealed ampoules and vials, and may be stored in a freeze-dried (lyophilized) condition requiring only the addition of the sterile liquid carrier, for example water for injections, immediately prior to use.
Preferred unit dosage formulations are those containing a daily dose or unit, daily sub-dose, or an appropriate fraction thereof, of an active ingredient.
Formulations of the SCI/MIP-1xcex1 proteins of the present invention preferably contain from 0.05 to 5 mg/ml of protein, for example 0.1 to 1.0 mg/ml. We have found that the solubility of the variants of the invention do vary although the maximum solubility of any one particular variant may be determined by simple titration by those of skill in the art.
The invention also provides such proteins and compositions for use in a method of treatment of the human or animal body.
The invention further provides a method for treating a subject who is to be exposed to an agent capable of killing dividing or cycling stem cells by administering to the subject an effective amount of a protein or composition according to the invention.
The subject may also be treated with a protein or composition according to the invention during or after chemotherapy. In the latter case, this will usually be for a period sufficient to allow clearance of the agent from the body.
The method of treatment according to the invention may be used in the treatment of solid tumours or leukemias. In the case of treatment of leukemias, it is possible to treat a sample of the patients bone marrow which has been removed from the body while the patient is undergoing treatment. The bone marrow is purged of cancer cells in the presence of a protein of composition according to the invention, and the treated marrow reintroduced into the patient.
Although the dose of the variant protein according to the invention will ultimately be at the discretion of the physician, taking into account the nature of the condition being treated and the state of the patient, effective doses may be in the range of from about 10 xcexcg/kg body weight to about 5 mg/kg of variant protein, for example from about 50 to about 1000 xcexcg/kg, eg about 500 xcexcg/kg.
We have also found that SCI/MIP1-xcex1 can act to enhance the expansion of primitive haemopoietic cells in ex vivo cytokine driven stem cell expansion experiments. Thus, variant proteins of the invention may also be used in methods to expand stem cell populations removed from a patient ex vivo wherein such stem cells are brought into contact with growth factors and the variant proteins of the invention under conditions which allow the growth and expansion in numbers of the cells, prior to reintroduction into the same or another patient. Such a method could be used in bone marrow transplant proceedures whereby a limited number of starting cells obtained from a donor are expanded prior to transplantation, or in certain therapies where a sample of bone marrow is removed from a patient prior to treatment and reintroduced following treatment. Such therapies include the treatment of leukemias, or other tumours including solid tumours where damage to the bone marrow may occur. The concentration of the variant proteins required to produce suitable activity will be in the range of from about 1 to about 100 ng/ml, for example from about 10 to about 50 ng/ml.
A protein or composition according to the invention may also be used in the treatment of disorders caused by proliferation of stem cells, eg. psoriasis.
A protein according to the invention is preferably a protein which contains at least one change from the native protein resulting in the loss of of one of more charges on the protein, eg. by replacement of one or more charged amino acids.
The change may be as a result of a deletion or substitution or insertion. In the case of a deletion or insertion, single base deletions or insertions are generally preferred, in order to retain a structure similar to the native protein. However, deletions of insertions of more than this, eg or 2, 3, 4, 5 or more amino acids are possible. In the case of a substitution, it is preferably a conservative substitution, such as Asp to Asn or Glu to Gln.
In addition, fragments of native protein which retain their stem cell inhibitory activity but which exhibit the reduced tendency to aggregate are within the scope or the invention.
Preferably, the change to the protein is in the C-terminal region, eg within the last 20 or even last 10 amino acids. This may include C-terminal deletions.
More than one change to a native stem cell inhibitor protein may be made. For example, 2, 3, 4 or 5 changes may be made.
Another preferred region of the MIP1 protein which may be altered is the putative heparin binding region between amino acids 68 and 71 of Seq. ID No. 1. We have determined by experimentation and by comparison of this sequence with known heparin binding regions that this portion of MIP1 has heparin binding activity. Thus suitable amino acids which may be altered in accordance with the invention include one, two or three of 68 (lys), 69 (arg) and 71 (arg). Such alterations may be made, if desired with an alteration to the c-terminal region of the MIP1 protein as described above.
Preferred stem cell inhibitor proteins of the invention are those based upon the human protein of Seq. ID. 2 or that of Seq. ID 3. Also preferred are the mature forms of such proteins, ie. from residues 28 onwards.
Particular amino acids which may be altered in the protein sequence of Seq. ID No.2 or Seq. ID No. 3 include alterations at any positively charged residue, eg. lys or arg, and/or at any negatively charged residue, eg asp or glu. The residues of Seq. ID. No. 2 which may be altered thus include: 29 (asp), 41 (arg), 50 (asp), 53 (glu), 60 (lys), 68 (lys), 69 (arg), 71 (arg), 76 (asp), 79 (glu), 80 (glu), 84 (lys), 87 (asp) or 90 (glu). The changes made to these positions may be as described above.
Combinations of changes which may be made include changing the final 2, 3, 4, 5 or 6 charged residues of the stem cell inhibitor. In the case of the human protein, this results in a protein which corresponds to the native protein except for changes at position 90 and/or one or more of positions 76, 79, 80, 84 or 88. Preferably, all the changes are single amino acid substitutions. Preferably, all such substitutions are conservative changes.
Proteins according to the invention may be made by any means available in the art. In the examples which follow, we have made modified stem cell inhibitory proteins by site directed mutagenesis using PCR primers of the murine SCI cDNA, followed by expression of the modified cDNA in a vector in a host cell to produce the protein. The protein may be recovered from the host cell using protein purification techniques known per se. Analogous methods may be used to make modified human or other primate SCI. The murine cDNA may be obtained for example by reference to the methods disclosed in WO89/10133 or by reference to the published literature. Human cDNA may also be obtained by reference to the published literature or cloned using probes based on all or part of the DNA sequence of Seq. ID No. 1 to identify SCI cDNA in a cDNA library made from cells expressing SCI RNA.
Accordingly, the present invention also provides a method for making a protein according to the invention which comprises:
(i) modifying a DNA sequence coding for SCI protein in order to introduce at least one change which causes a change in the amino acid sequence of the SCI protein;
(ii) expressing said DNA, operably linked to a promoter, in a vector in a host cell compatible with said promoter; and
(iii) recovering said protein.
The DNA may be modified by site directed mutagenesis as mentioned above or described in the examples, to obtain insertions, deletions or subsitutions in the amino acid sequence.
The vector may contain one or more selectable marker genes, for example an ampicillin resistance gene in the case of a bacterial plasmid or a neomycin resistance gene for a mammalian vector.
A further embodiment of the invention provides host cells transformed or transfected with the vectors for the replication and expression of DNA produced as described above, including the DNA Seq. ID No. 1 modified as mentioned above. The cells will be chosen to be compatible with the vector and may for example be bacterial, yeast, insect or mammalian.
The invention also provides monoclonal or polyclonal antibodies to a peptide according to the invention which is directed to a epitope containing an alteration of the native SCI. The invention further provides a process for the production of such monoclonal or polyclonal antibodies. Monoclonal antibodies may be prepared by conventional hybridoma technology using the proteins or peptide fragments thereof, as an immunogen. Polyclonal antibodies may also be prepared by conventional means which comprise inoculating a host animal, for example a rat or a rabbit, with a peptide of the invention and recovering immune serum.
In either case, antibodies which recognise altered epitopes may be identified by screening them with native SCI and the altered SCI to which the antibody was raised and identifying an antibody which recognises only the altered SCI.
The following examples illustrate the invention.